The present invention relates to an improved latch needle for a knitting machine.
By operating on the needle butt, cams position the needle at the required height for knitting, tucking, welting and so on.
The latch spoon is pivotally mounted to the shank for movement between two limiting positions which are angularly spaced approximately 150xc2x0 apart. In the first position the latch spoon covers the point of the hook and in the second position the latch spoon rests against the shank in generally parallel relationship with the shank.
The latch needle is self-actuating since the opening and closing of the hook is accomplished through pressure of a loop upon the latch as the needle rises and falls relative to the loop.
The latch needle was invented in 1849 and enabled simple knitting machines to be built which were capable of high speed.
Latch needles have a wide variety of applications such as the knitting of socks and fine gauge hosiery, underwear and outerwear knitted on circular and flat machines, lace knitted on straight bar machines as well as narrow fabrics, ribbons, tapes and so on.
The success of the latch needle has been largely due to the simplicity of the loop forming action supported by improvements in precision engineering and the enormous resources which have gone into the development of needle technology.
The main disadvantages of latch needles currently in use are:
1. The extent of the movement needed to swing the latch through approximately 150xc2x0 in clearing a newly formed loop off the end of the latch slows the rate of operation obtainable.
2. When the needle moves upwards and the latch opens to clear a newly formed loop, the shape of the needle and latch, together with the upward movement, cause the knitted loop to rise up with the needle. Therefore a holding down sinker is necessary to restrain the previously knitted loop from rising up with the needle and latch.
3. When the latch closes on to the point of the hook at high speed there can be a problem of impact damage which eventually causes fracture of the hook.
4. Since the loop controls the opening and closing of the latch, an empty needle requires an additional mechanism to open the latch in situations such as the commencement of a new garment or when a loop is transferred to an adjacent needle.
The latch is also uncontrolled when the needle rises to clear the xe2x80x9coldxe2x80x9d loop off the end of the latch, requiring a latch guard which obscures vision and prevents easy access for yam threading and general attention. Latch guards and fixing brackets around the needle cylinder of a circular knitting machine provides points for the accumulation of lint and dust which is detrimental to efficiency.
Attempts have been made previously to restrict the angle through which a latch pivots. GB 1160832 represents a typical earlier approach in that the latch is caused to pivot by an amount sufficient to bridge the gap between the point of the hook and the inside of the neck of the needle so that the hook is closed from the inside instead of being closed from the outside.
GB 1416291 is another patent disclosing latch movement between two end positions in the first of which the latch is in contact, at its free end, with the inner surface of the hook to close the hook and in the second of which the latch rests against a stop provided on the shank of the needle.
In the prior art discussed above, the hook closing action is from the needle shank towards the hook. Hence, when the needle is in use, if a new yarn is not located securely within the upper part of the hook, the in-to-out action by the latch tends to push the yarn outside the hook. Further, on circular knitting machines, the placing of new yarn in to the hook would require a loop forming sinker which would tend to reduce the productive capacity overall.
An object of the present invention is to provide an improved latch needle which aims to overcome these disadvantages.
According to the broadest aspect of the present invention there is provided a latch needle having a hook, a stem and a latch, the hook and the latch being movable one relative to the other between two positions in the first of which the latch is located within the hook and in the second of which the latch is located external of the hook and means fur creating relative movement between the hook and the latch.
In a preferred embodiment of the invention the hook and stem are fixed, the latch being movable relative thereto. In the preferred embodiment also the latch is pivoted to the stem such that the tip of the latch can press the tip of the hook to oscillate, in an arc, between positions internal and external of the tip of the hook
The tip of the latch spoon may be notched to permit the latch to pass either side of the point of the hook. One or more cavities may be provided in the stem and/or hook to receive the notched spoon. Alternatively, the lip of the latch can pass the tip of the hook in an inter-fitting tongued relationship, preferably with overlapping of the tips of the hooks and latch as viewed in one elevation and clearance between the hook and latch as viewed in a second elevation.
In the preferred embodiment of the invention the latch is moved relative to the hook by means of a lug formed on one side of the latch. Preferably the lug is held in the recess of a slider which is positioned along side the needle. Axial movement of the slider relative to the needle causes radial movement of the lug, and hence the latch. Conveniently, butts, provided on the needle and slider engage in associated cam tracks to control the positions of the slider and needle. Alternatively, the lug itself may be held in a cam track.
In another embodiment of the invention, the latch is moved relative to the hook by means of lugs formed on either side of the latch. An auxiliary sinker is provided with control faces which act on the lugs. Alternatively the latch may be moved electromagnetically or in any other convenient manner.
Whichever way the latch is moved, the extent of its arcuate movement is approximately 40 degrees.
During knitting, yarns are subjected to various stresses and strains which can cause them to slip out of the confines of a hook. An important feature of conventional latch needles is the ability of the latch to secure newly fed yarn into the hook and retain it there, this feature being maintained in the latch needle of the invention. In this respect the closing of the hook from outside to inside is an important feature since the open latch guides yam into the hook, further rotation of the latch retaining the yam in the hook.